I had this problem after we lost a domain name for a Joomla! site.
I copied the Joomla! site back onto the server using a new domain name, which allowed us to use the same database. There were two issues:
– I had to change some configuration settings, but Joomla! reported that it couldn’t save configuration.php. I ended up changing it via Filezilla.
– Virtuemart displayed nothing until it was configured to use the new domain name (see this post on that topic.)
Once I had the site running and looking ok I had to update the theme. This was impossible because of the write permissions issue. I couldn’t write to any location on the server via Joomla! I tried everything in this useful post, but no joy.
The website is running on IIS 6.
I found a setting on the hosting site’s control panel called ‘Website Write Permissions’, and ticked it. This fixed the Joomla! write permissions, but what else does it do?
Next step: update to the latest versions of Joomla! and Virtuemart, and urgently review site security.